The present invention relates generally to circuits and techniques for controlling current-mode circuits such as amplifiers, mixers and the like. More particularly, the present invention has found specific advantageous application in circuit environments where current-mode circuits are sensitive to voltage excursions at input and/or output ports thereof.
The electronics industry continues to strive for high-powered, high-functioning circuits. Significant achievements in this regard have been realized through the fabrication of very large-scale integration of circuits on small areas of silicon wafer. For applications directed to high-frequency communications, main objectives in the design and manufacturing of such devices are typically directed to obtaining circuitry that occupies as small an area and uses the smallest amount of power as practicable, while at the same time preserving the integrity of the data being communicated by the signal.
One type of circuit often used in connection with communications applications is commonly referred to as a current-mode circuit. A current-mode circuit is used in a wide variety of electronic products including, but not limited to, global positioning (GPS) receivers, cordless and cellular phone circuits, wireless local area networks and other types of mobile communication receivers and transmitters (xe2x80x9ctransceiversxe2x80x9d).
With current-mode circuits, the current amplification is taken into account and the nonlinearity in the voltage swing is not important. In such a circuit, should DC coupling to another circuit block be required, the overall operation of the circuit may be susceptible to an unwanted DC voltage due to a significant nonlinearity in voltage swing associated with the DC coupling. This unwanted DC voltage can saturate the output of the circuit block and thereby severely degrade the overall operation.
Such DC voltage influences can cause unacceptable operation in various types of communications applications, such as radio frequency (RF), intermediate frequency (IF) and the low frequency, and/or in connection with base-band signal processing. For example, in a power mixer circuit, any extraneous DC current flowing into the final mixer stage can result in an intolerably large increase in current consumption and, in some circuit designs, unacceptable signal distortion.
In a typical current-mode circuit block, the output impedance of each functional block is preferably as high as possible. Ideally, each functional block is designed with an output impedance that mimics an ideal current source and with an input impedance that tracks a zero-Ohm circuit. Main objectives in the design of such circuits include controlling the input and output impedance levels and maintaining the voltage at desirable levels. Failing to maintain the input impedance, the output impedance or the control voltage can result in huge increases in power consumption and other operational disadvantages including, for example, significant increases in noise and degradations in linearity performance.
Accordingly, there is a need to provide a current-mode circuit and technique that overcomes the above-mentioned disadvantages.
The present invention is implemented in various embodiments directed to addressing the above applications and concerns, as well as other advantages that will become apparent upon a careful review of the following discussion. For example, certain aspects of the invention are directed to advantages discovered in connection with controlling current passing between cascaded current-mode blocks by using a feedback loop to control DC voltage levels at the interface between the current-mode blocks. Appropriately implemented, this approach can result in a number advantages relating to improvements in terms of reductions in power consumption and mitigation of other problems relating to, for example, dynamic range and linearity.
According to a particular example application, the present invention includes first and second cascaded current-mode circuit blocks, and a circuit-replication and comparison block adapted to replicate the operation and output impedance of the first current-mode circuit block and to replicate the operation and input impedance of the second current-mode circuit block. The replication-comparison block can be implemented to include a differential comparator adapted to detect and correct for a voltage differential corresponding to current passing from the first current-mode circuit block and the second current-mode circuit block. This approach can result in a number advantages relating to improvements in terms of various operational aspects including, for example, reductions in power consumption.
The above summary is not intended to provide an overview of all aspects of the present invention. Other aspects of the present invention are exemplified and described in connection with the detailed description.